Delta-aminolevulinic acid transport by intestinal and renal peptide transporters and its physiological and clinical implications

Cefadroxil Targeting of SLC15A2/PEPT2 Protects From Colistin Nephrotoxicity

Acute kidney injury (AKI) and chronic kidney disease (CKD) are considered interconnected syndromes, as AKI episodes may accelerate CKD progression, and CKD increases the risk of AKI. Genome-wide association studies (GWAS) may identify novel actionable therapeutic targets. Human GWAS for AKI or CKD were combined with murine AKI transcriptomics data sets to identify 13 (ACACB, ACSM5, CNDP1, DPEP1, GATM, SLC6A12, AGXT2L1, SLC15A2, CTSS, ICAM1, ITGAX, ITGAM, and PPM1J) potentially actionable therapeutic targets to modulate kidney disease severity across species and the AKI-CKD spectrum. Among them, SLC15A2, encoding the cell membrane proton-coupled peptide transporter 2, was prioritized for data mining and functional intervention studies in vitro and in vivo because of its known function to transport nephrotoxic drugs such as colistin and the possibility for targeting with small molecules already in clinical use, such as cefadroxil. Data mining disclosed that SLC15A2 was upregulated in the tubulointerstitium of human CKD, including diabetic nephropathy, and the upregulation was localized to proximal tubular cells. Colistin elicited cytotoxicity and proinflammatory response in cultured human and murine proximal tubular cells that was decreased by concomitant exposure to cefadroxil. In proof-of-concept in vivo studies, cefadroxil protected from colistin nephrotoxicity in mice. The GWAS association of SLC15A2 with human kidney disease may be actionable and related to the modifiable transport of nephrotoxins causing repeated subclinical episodes of AKI and/or chronic nephrotoxicity.

Tumor Cell Membrane-Encapsulated MLA Solid Lipid Nanoparticles for Targeted Diagnosis and Radiosensitization Therapy of Cutaneous Squamous Cell Carcinoma

Squamous cell carcinoma (SCC) is a common nonmelanoma skin cancer. Radiotherapy plays an integral role in treating SCC due to its characteristics, such as diminished intercellular adhesion, heightened cell migration and invasion capabilities, and immune evasion. These problems lead to inaccurate tumor boundary positioning and radiotherapy tolerance in SCC treatment. Thus, accurate localization and enhanced radiotherapy sensitivity are imperative for effective SCC treatment. To address the existing limitations in SCC therapy, we developed monoglyceride solid lipid nanoparticles (MG SLNs) and enveloped them with the A431 cell membrane (A431 CM) to create A431@MG. The characterization results showed that A431@MG was spherical. Furthermore, A431@MG had specific targeting for A431 cells. In A431 tumor-bearing mice, A431@MG demonstrated prolonged accumulation within tumors, ensuring precise boundary localization of SCC. We further advanced the approach by preparing MG SLNs encapsulating 5-aminolevulinic acid methyl ester (MLA) and desferrioxamine (DFO) with an A431 CM coating to yield A431@MG-MLA/DFO. Several studies have revealed that DFO effectively reduced iron content, impeding protoporphyrin IX (PpIX) biotransformation and promoting PpIX accumulation. Simultaneously, MLA was metabolized into PpIX upon cellular entry. During radiotherapy, the heightened PpIX levels enhanced reactive oxygen species (ROS) generation, inducing DNA and mitochondrial damage and leading to cell apoptosis. In A431 tumor-bearing mice, the A431@MG-MLA/DFO group exhibited notable radiotherapy sensitization, displaying superior tumor growth inhibition. Combining A431@MG-MLA/DFO with radiotherapy significantly improved anticancer efficacy, highlighting its potential to serve as an integrated diagnostic and therapeutic strategy for SCC.

RNA interference therapy in acute hepatic porphyrias

The acute hepatic porphyrias (AHPs) are inherited disorders of heme biosynthesis characterized by life-threatening acute neurovisceral attacks precipitated by factors that upregulate hepatic 5-aminolevulinic acid synthase 1 (ALAS1) activity. Induction of hepatic ALAS1 leads to the accumulation of porphyrin precursors, in particular 5-aminolevulinic acid (ALA), which is thought to be the neurotoxic mediator leading to acute attack symptoms such as severe abdominal pain and autonomic dysfunction. Patients may also develop debilitating chronic symptoms and long-term medical complications, including kidney disease and an increased risk of hepatocellular carcinoma. Exogenous heme is the historical treatment for attacks and exerts its therapeutic effect by inhibiting hepatic ALAS1 activity. The pathophysiology of acute attacks provided the rationale to develop an RNA interference therapeutic that suppresses hepatic ALAS1 expression. Givosiran is a subcutaneously administered N-acetylgalactosamine-conjugated small interfering RNA against ALAS1 that is taken up nearly exclusively by hepatocytes via the asialoglycoprotein receptor. Clinical trials established that the continuous suppression of hepatic ALAS1 mRNA via monthly givosiran administration effectively reduced urinary ALA and porphobilinogen levels and acute attack rates and improved quality of life. Common side effects include injection site reactions and increases in liver enzymes and creatinine. Givosiran was approved by the US Food and Drug Administration and European Medicines Agency in 2019 and 2020, respectively, for the treatment of patients with AHP. Although givosiran has the potential to decrease the risk of chronic complications, long-term data on the safety and effects of sustained ALAS1 suppression in patients with AHP are lacking.

Proton-Coupled Oligopeptide Transport (Slc15) in the Brain: Past and Future Research

This mini-review describes the role of the solute carrier (SLC)15 family of proton-coupled oligopeptide transporters (POTs) and particularly Pept2 (Slc15A2) and PhT1 (Slc15A4) in the brain. That family transports endogenous di- and tripeptides and peptidomimetics but also a number of drugs. The review focuses on the pioneering work of David E. Smith in the field in identifying the impact of PepT2 at the choroid plexus (the blood-CSF barrier) as well as PepT2 and PhT1 in brain parenchymal cells. It also discusses recent findings and future directions in relation to brain POTs including cellular and subcellular localization, regulatory pathways, transporter structure, species differences and disease states.

Molecular Insights to the Structure-Interaction Relationships of Human Proton-Coupled Oligopeptide Transporters (PepTs)

Human proton-coupled oligopeptide transporters (PepTs) are important membrane influx transporters that facilitate the cellular uptake of many drugs including ACE inhibitors and antibiotics. PepTs mediate the absorption of di- and tri-peptides from dietary proteins or gastrointestinal secretions, facilitate the reabsorption of peptide-bound amino acids in the kidney, and regulate neuropeptide homeostasis in extracellular fluids. PepT1 and PepT2 have been the most intensively investigated of all PepT isoforms. Modulating the interactions of PepTs and their drug substrates could influence treatment outcomes and adverse effects with certain therapies. In recent studies, topology models and protein structures of PepTs have been developed. The aim of this review was to summarise the current knowledge regarding structure-interaction relationships (SIRs) of PepTs and their substrates as well as the potential applications of this information in therapeutic optimisation and drug development. Such information may provide insights into the efficacy of PepT drug substrates in patients, mechanisms of drug-drug/food interactions and the potential role of PepTs targeting in drug design and development strategies.

Sodium Ferrous Citrate and 5-Aminolevulinic Acid Exert a Therapeutic Effect on Endotoxin-Induced Uveitis in Rats

The metabolism of 5-aminolevulinic acid (ALA) is more efficient when combined with sodium ferrous citrate (SFC). Our previous study revealed that oral administration of ALA, which has anti-inflammatory properties, and SFC (ALA/SFC) immediately before lipopolysaccharide (LPS) inoculation suppressed endotoxin-induced uveitis (EIU) in rats. However, the therapeutic effect of ALA/SFC post-administration remains unexplored. Hence, this study aimed to evaluate the therapeutic efficacy of ALA/SFC on EIU in rats, which were administered with a gastric gavage of ALA/SFC (100/157 mg/kg) or prednisolone (Pred, 10 mg/kg) after 4 h of LPS inoculation. The treatment groups showed ameliorated clinical scores, inflammatory cells, protein levels in the aqueous humor (AqH), and histopathologic evaluation 24 h after LPS inoculation. Furthermore, the treatment groups had reduced tumor necrosis factor-α, nitric oxide, prostaglandin E2, and interleukin-6 levels in the AqH. ALA/SFC demonstrated an anti-inflammatory effect equivalent to that demonstrated by Pred. These findings indicate that ALA/SFC exerts a therapeutic effect on EIU in rats, indicating its clinical usefulness in uveitis treatment.

5-Aminolevulinic acid increases boronophenylalanine uptake into glioma stem cells and may sensitize malignant glioma to boron neutron capture therapy

Boron neutron capture therapy (BNCT) is a high-LET particle radiotherapy clinically tested for treating malignant gliomas. Boronophenylalanine (BPA), a boron-containing phenylalanine derivative, is selectively transported into tumor cells by amino acid transporters, making it an ideal agent for BNCT. In this study, we investigated whether the amino acid 5-aminolevulinic acid (ALA) could sensitize glioma stem cells (GSCs) to BNCT by enhancing the uptake of BPA. Using human and mouse GSC lines, pre-incubation with ALA increased the intracellular accumulation of BPA dose-dependent. We also conducted in vivo experiments by intracerebrally implanting HGG13 cells in mice and administering ALA orally 24 h before BPA administration (ALA + BPA-BNCT). The ALA preloading group increased the tumor boron concentration and improved the tumor/blood boron concentration ratio, resulting in improved survival compared to the BPA-BNCT group. Furthermore, we found that the expression of amino acid transporters was upregulated following ALA treatment both in vitro and in vivo, particularly for ATB0,+. This suggests that ALA may sensitize GSCs to BNCT by upregulating the expression of amino acid transporters, thereby enhancing the uptake of BPA and improving the effectiveness of BNCT. These findings have important implications for strategies to improve the sensitivity of malignant gliomas to BPA-BNCT.

A Thiosemicarbazone Derivative as a Booster in Photodynamic Therapy-A Way to Improve the Therapeutic Effect

Photodynamic therapy is one of the most patient friendly and promising anticancer therapies. The active ingredient is irradiated protoporphyrin IX, which is produced in the body that transfers energy to the oxygen-triggering phototoxic reaction. This effect could be enhanced by using iron chelators, which inhibit the final step of heme biosynthesis, thereby increasing the protoporphyrin IX concentration. In the presented work, we studied thiosemicarbazone derivative, which is a universal enhancer of the phototoxic effect. We examined several genes that are involved in the transport of the heme substrates and heme itself. The results indicate that despite an elevated level of ABCG2, which is responsible for the PpIX efflux, its concentration in a cell is sufficient to trigger a photodynamic reaction. This effect was not observed for 5-ALA alone. The analyzed cell lines differed in the scale of the effect and a correlation with the PpIX accumulation was observed. Additionally, an increased activation of the iron transporter MFNR1 was also detected, which indicated that the regulation of iron transport is essential in PDT.

The effect of hypoxia on photodynamic therapy with 5-aminolevulinic acid in malignant gliomas

BACKGROUND

Glioblastoma (GBM) is a high-grade, poor prognosis tumor that is resistant to standard treatment. The presence of a small number of glioma stem cells (GSCs) surviving in the harsh microenvironment is responsible for their refractoriness. This study aimed to investigate the effect of a hypoxic environment on the sensitivity of GSCs to photodynamic therapy with 5-aminolevulinic acid (ALA-PDT).

MATERIALS AND METHODS

Six human GSC lines, Mesenchymal types HGG13, HGG30, HGG1123, and Proneural types HGG146, HGG157, HGG528, were divided into two groups: normoxia (O₂ 21%)-cultured cells (Normoxia-GSCs), and hypoxia (O₂ 5%)-cultured cells (Hypoxia-GSCs). To compare the effects of different oxygen partial pressures on photoporphyrin Ⅸ (PpⅨ) biosynthetic activity, PpⅨ biosynthetic enzyme and transporter expression levels were examined by qRT-PCR; the intracellular PpⅨ concentration was determined using flow cytometry. Additionally, the sensitivity of these two groups of cells to ALA-PDT was evaluated in vitro.

RESULTS

Hypoxia-GSCs showed higher mRNA levels of FECH (ferrochelatase), which is required for iron synthesis to convert PpⅨ to heme, compared with Normoxia-GSCs. Flow cytometry revealed that the accumulation of PpⅨ in Hypoxia-GSCs reduced upon incubation with ALA. However, Hypoxia-GSCs showed less reduction in sensitivity to ALA-PDT than Normoxia-GSCs.

CONCLUSION

Hypoxia-GSCs had lower intracellular PpⅨ accumulation than Normoxia-GSCs due to increased gene expression of FECH, and that their sensitivity to ALA-PDT was reduced less, despite accumulating lower concentrations of PpⅨ. ALA-PDT is a potentially effective therapy for hypoxia-tolerant GSCs that exist in hypoxia at 5% oxygen concentration.

Heterologous (Over) Expression of Human SoLute Carrier (SLC) in Yeast: A Well-Recognized Tool for Human Transporter Function/Structure Studies

For more than 20 years, yeast has been a widely used system for the expression of human membrane transporters. Among them, more than 400 are members of the largest transporter family, the SLC superfamily. SLCs play critical roles in maintaining cellular homeostasis by transporting nutrients, ions, and waste products. Based on their involvement in drug absorption and in several human diseases, they are considered emerging therapeutic targets. Despite their critical role in human health, a large part of SLCs' is 'orphans' for substrate specificity or function. Moreover, very few data are available concerning their 3D structure. On the basis of the human health benefits of filling these knowledge gaps, an understanding of protein expression in systems that allow functional production of these proteins is essential. Among the 500 known yeast species, S. cerevisiae and P. pastoris represent those most employed for this purpose. This review aims to provide a comprehensive state-of-the-art on the attempts of human SLC expression performed by exploiting yeast. The collected data will hopefully be useful for guiding new attempts in SLCs expression with the aim to reveal new fundamental data that could lead to potential effects on human health.

Identification and pharmacological modification of resistance mechanisms to protoporphyrin-mediated photodynamic therapy in human cutaneous squamous cell carcinoma cell lines

BACKGROUND

Photodynamic therapy (PDT) is clinically approved to treat neoplastic skin diseases such as precursors of cutaneous squamous cell carcinoma (cSCC). In PDT, 5-aminolevulinic acid (5-ALA) drives the selective formation of the endogenous photosensitizer protoporphyrin IX (PpIX). Although 5-ALA PDT is clinically highly effective, resistance might occur due to decreased accumulation of PpIX in certain tumors. Such resistance may be caused by any fundamental step of PpIX accumulation: 5-ALA uptake, PpIX synthesis and PpIX efflux.

METHODS

We investigated PpIX accumulation and photodynamically induced cell death in PDT refractory SCC-13, PDT susceptible A431, and normal human epidermal keratinocytes (NHEK). Expression of genes associated with cellular PpIX kinetics was investigated on mRNA and protein level. PpIX accumulation and cell death upon illumination were pharmacologically manipulated using drugs targeting 5-ALA uptake, PpIX synthesis or efflux.

RESULTS

The experiments indicate that taurine transporter (SLC6A6) is the major pathway for 5-ALA uptake in cSCC cells, while being less important in NHEK. Downregulation of PpIX synthesis enzymes in SCC-13 was counteracted by methotrexate (MTX) treatment, which restored PpIX formation and cell death. PpIX efflux inhibitors targeting ABC transporters led to significantly increased PpIX accumulation in SCC-13, thereby fully overcoming resistance.

CONCLUSIONS

The results indicate a conserved threshold for PpIX accumulation with respect to PDT-resistance. Cells showed increased viability after PDT at PpIX concentrations below 1.5 nM. Selective uptake of 5-ALA via taurine transporter SLC6A6 in cutaneous tumor cells is novel but unrelated to resistance. MTX can partially abrogate resistance by PpIX synthesis enzyme induction, while efflux mechanisms via ABC transporters seem the main driving force and promising drug targets.

An Intracellular Self-Assembly-Driven Uninterrupted ROS Generator Augments 5-Aminolevulinic-Acid-Based Tumor Therapy

Free radical therapy based on 5-aminolevulinic acid (ALA, a precursor of the photosensitizer protoporphyrin IX (PpIX)) has been approved by the US Food and Drug Administration for clinical tumor treatment. However, PpIX can be quickly converted into photoinactive heme, leading to unexpectedly paused production of free radicals and severely hindering its therapeutic benefits. Here, inspired by the natural biotransformation of ALA (ALA-PpIX-heme), an uninterrupted reactive oxygen species generator (URG) that converts useless heme to peroxidase mimics via intracellular self-assembly is developed. The URG is prepared by enwrapping ALA-loaded polyamide-amine dendrimers in red blood cell membrane vesicles with a further surface modification of G-quadruplex-structured AS1411. The URGs realize "¹ O₂ -•OH" uninterrupted generation through "recycling waste" in two steps: i) PpIX generates ¹ O₂ under laser irradiation; and ii) the photoinactive metabolite heme self-assembled with AS1411 to catalyze H₂ O₂ conversion into •OH. Interestingly, the specific generation of ¹ O₂ in mitochondria and •OH in nuclei further augments the free-radical-induced damage. It is demonstrated that URG can continuously produce free radicals for 6 h postirradiation, and shows 3.3-times more than that of the nonassembly group, achieving nearly 80% regression of tumors in vivo.

Functional characterization of Atlantic salmon (Salmo salar L.) PepT2 transporters

Abstract

The high‐affinity/low‐capacity system Slc15a2 (PepT2) is responsible for the reuptake of di/tripeptides from the renal proximal tubule, but it also operates in many other tissues and organs. Information regarding PepT2 in teleost fish is limited and, to date, functional data are available from the zebrafish (Danio rerio) only. Here, we report the identification of two slc15a2 genes in the Atlantic salmon (Salmo salar) genome, namely slc15a2a and slc15a2b. The two encoded PepT2 proteins share 87% identity and resemble both structurally and functionally the canonical vertebrate PepT2 system. The mRNA tissue distribution analyses reveal a widespread distribution of slc15a2a transcripts, being more abundant in the brain and gills, while slc15a2b transcripts are mainly expressed in the kidney and the distal part of the gastrointestinal tract. The function of the two transporters was investigated by heterologous expression in Xenopus laevis oocytes and two‐electrode voltage‐clamp recordings of transport and presteady‐state currents. Both PepT2a and PepT2b in the presence of Gly‐Gln elicit pH‐dependent and Na⁺ independent inward currents. The biophysical and kinetic analysis of the recorded currents defined the transport properties, confirming that the two Atlantic salmon PepT2 proteins behave as high‐affinity/low‐capacity transporters. The recent structures and the previous kinetic schemes of rat and human PepT2 qualitatively account for the characteristics of the two Atlantic salmon proteins. This study is the first to report on the functional expression of two PepT2‐type transporters that operate in the same vertebrate organism as a result of (a) gene duplication process(es).

Key points

Two slc15a2‐type genes, slc15a2a and slc15a2b coding for PepT2‐type peptide transporters were found in the Atlantic salmon.

slc15a2a transcripts, widely distributed in the fish tissues, are abundant in the brain and gills, while slc15a2b transcripts are mainly expressed in the kidney and distal gastrointestinal tract.

Amino acids involved in vertebrate Slc15 transport function are conserved in PepT2a and PepT2b proteins.

Detailed kinetic analysis indicates that both PepT2a and PepT2b operate as high‐affinity transporters.

The kinetic schemes and structures proposed for the mammalian models of PepT2 are suitable to explain the function of the two Atlantic salmon transporters.

Detection of Canine Urothelial Carcinoma Cells in Urine Using 5-Aminolevulinic Acid

This study aimed to establish a method to detect canine urothelial carcinoma cells in urine using 5-aminolevulinic acid (5-ALA) and to evaluate its diagnostic accuracy. Urine samples were collected from 21 dogs diagnosed with urothelial carcinoma and three urothelial carcinoma cell lines were used. Urine samples obtained from seven healthy dogs were used as controls. Cells in the urine sediment, or urothelial carcinoma cell lines, were cultured with 5-ALA and then observed under a fluorescence microscope. Moreover, we examined the relationship between fluorescence intensity and the presence of metastasis as well as tumor invasion into the bladder wall in cases of urothelial carcinoma. Urine-derived cells from urothelial carcinoma and urothelial carcinoma cell lines showed clearer red fluorescence with the addition of 5-ALA compared to that exhibited by the cells from healthy dogs. The sensitivity and specificity of the diagnosis of urothelial carcinoma were 90% and 86%, respectively. Significant associations were found between fluorescence intensity and tumor metastasis and bladder wall invasion. This study showed that 5-ALA can be used to detect urothelial carcinoma cells in dogs with relatively high diagnostic accuracy. Further, the fluorescence intensity of tumor cells caused by 5-ALA correlated with the clinical condition of urothelial carcinoma cases, which suggested that 5-ALA could be used as a prognostic marker for canine urothelial carcinoma.

Analysis of Factors Affecting 5-ALA Fluorescence Intensity in Visualizing Glial Tumor Cells-Literature Review

Glial tumors are one of the most common lesions of the central nervous system. Despite the implementation of appropriate treatment, the prognosis is not successful. As shown in the literature, maximal tumor resection is a key element in improving therapeutic outcome. One of the methods to achieve it is the use of fluorescent intraoperative navigation with 5-aminolevulinic acid. Unfortunately, often the level of fluorescence emitted is not satisfactory, resulting in difficulties in the course of surgery. This article summarizes currently available knowledge regarding differences in the level of emitted fluorescence. It may depend on both the histological type and the genetic profile of the tumor, which is reflected in the activity and expression of enzymes involved in the intracellular metabolism of fluorescent dyes, such as PBGD, FECH, UROS, and ALAS. The transport of 5-aminolevulinic acid and its metabolites across the blood–brain barrier and cell membranes mediated by transporters, such as ABCB6 and ABCG2, is also important. Accompanying therapies, such as antiepileptic drugs or steroids, also have an impact on light emission by tumor cells. Accurate determination of the factors influencing the fluorescence of 5-aminolevulinic acid-treated cells may contribute to the improvement of fluorescence navigation in patients with highly malignant gliomas.

Cloning of oligopeptide transport carrier PepT2 and comparative analysis of PepT2 expression in response to dietary nitrogen levels in yak and cattle

The objectives of this study were clone oligopeptide transport carrier PepT2 and compare its abundance in kidney tissues of yak and cattle in response to different dietary nitrogen levels. Four adult female yaks were enrolled as donor animals for profiling the molecular characteristics and expression specificity of yak PepT2 (yPepT2), and twenty-four castrated males of each of two genotypes, yak (Bos grunniens) and indigenous cattle (Bos taurus) were used to explore PepT2 mRNA expression in kidney tissue in different nitrogen (N) levels (10.3, 19.5, 28.5 or 37.6 g N/kg dry matter; DM). Our results showed that the yPepT2 coding sequence region contains 2190 bp, and encodes a putative protein of 729 amino acids (AA) residues. The yPepT2 AA sequence identified eight putative extracellular N-glycosylation sites (Asn7, Asn80, Asn373, Asn435, Asn472, Asn508, Asn528, Asn587) and eight intracellular putative protein kinase C sites (Ser34, Ser264, Ser274, Ser376, Ser442, Ser586, Ser640, Ser724). The yPepT2 AA sequence was 98 and 94% identical to PepT2 from zebu cattle (Bos indicus) and sheep (Ovis aries), respectively. The relative PepT2 expression in kidney tissue for yak was greater than of indigenous cattle in the10.3 and 28.5 N/kg DM diet, but it was lower for yaks in 37.6 N/kg DM diet. These implied that relative PepT2 mRNA expression was higher in yak kidney than that in indigenous cattle at lower dietary N supplies, but more research on PepT2 will be required to determine the renal regulatory mechanisms.

Recurrent Seizures in an Adolescent Female-A Daunting Puzzle

Acute porphyrias are metabolic disorders resulting from deficiency of a specific enzyme involved in heme biosynthetic pathway. These deficiencies also affect normal renal physiology, as kidneys are also involved in heme synthesis. Sometimes, this could even lead to end stage renal disease. Acute Intermittent Porphyria, an autosomal dominant disorder arising from half-normal activity of hydroxymethylbilane synthase, is characterized by occurrence of vague neurovisceral attacks (abdominal pain, nausea, vomiting, constipation and neuropsychiatric symptoms), with urinary excretion of porphyrin precursors, such as 5-Amino-levulinic acid (ALA) and Porphobilinogen (PBG). Acute attacks are triggered by dehydration, diarrhea, steroids, low calorie diets. Treatment includes avoidance of precipitating factors, adequate hydration, high carbohydrate diet and heme replacement. Here, we present an adolescent female who had presented with recurrent abdominal pain, dyselectrolyemia with associated seizures, was diagnosed with Acute Intermittent Porphyria and recovered well with symptomatic management.

Boosting 5-ALA-based photodynamic therapy by a liposomal nanomedicine through intracellular iron ion regulation

5-Aminolevulinic acid (5-ALA) has been approved for clinical photodynamic therapy (PDT) due to its negligible photosensitive toxicity. However, the curative effect of 5-ALA is restricted by intracellular biotransformation inactivation of 5-ALA and potential DNA repair of tumor cells. Inspired by the crucial function of iron ions in 5-ALA transformation and DNA repair, a liposomal nanomedicine (MFLs@5-ALA/DFO) with intracellular iron ion regulation property was developed for boosting the PDT of 5-ALA, which was prepared by co-encapsulating 5-ALA and DFO (deferoxamine, a special iron chelator) into the membrane fusion liposomes (MFLs). MFLs@5-ALA/DFO showed an improved pharmaceutical behavior and rapidly fused with tumor cell membrane for 5-ALA and DFO co-delivery. MFLs@5-ALA/DFO could efficiently reduce iron ion, thus blocking the biotransformation of photosensitive protoporphyrin IX (PpIX) to heme, realizing significant accumulation of photosensitivity. Meanwhile, the activity of DNA repair enzyme was also inhibited with the reduction of iron ion, resulting in the aggravated DNA damage in tumor cells. Our findings showed MFLs@5-ALA/DFO had potential to be applied for enhanced PDT of 5-ALA.

Potential of Photodynamic Therapy Based on Sugar-Conjugated Photosensitizers

In 2015, the Japanese health insurance approved the use of a second-generation photodynamic therapy (PDT) using talaporfin sodium (TS); however, its cancer cell selectivity and antitumor effects of TS PDT are not comprehensive. The Warburg effect describes the elevated rate of glycolysis in cancer cells, despite the presence of sufficient oxygen. Because cancer cells absorb considerable amounts of glucose, they are visible using positron emission tomography (PET). We developed a third-generation PDT based on the Warburg effect by synthesizing novel photosensitizers (PSs) in the form of sugar-conjugated chlorins. Glucose-conjugated (tetrafluorophenyl) chlorin (G-chlorin) PDT revealed significantly stronger antitumor effects than TS PDT and induced immunogenic cell death (ICD). ICD induced by PDT enhances cancer immunity, and a combination therapy of PDT and immune checkpoint blockers is expected to synergize antitumor effects. Mannose-conjugated (tetrafluorophenyl) chlorin (M-chlorin) PDT, which targets cancer cells and tumor-associated macrophages (TAMs), also shows strong antitumor effects. Finally, we synthesized a glucose-conjugated chlorin e6 (SC-N003HP) that showed 10,000-50,000 times stronger antitumor effects than TS (IC₅₀) in vitro, and it was rapidly metabolized and excreted. In this review, we discuss the potential and the future of next-generation cancer cell-selective PDT and describe three types of sugar-conjugated PSs expected to be clinically developed in the future.

5-Aminolevulinic acid for fluorescence-guided surgery in pancreatic cancer: Cellular transport and fluorescence quantification studies

5-Aminolevulinic acid (ALA) is a potential contrast agent for fluorescence-guided surgery in pancreatic ductal adenocarcinoma (PDAC). However, factors influencing ALA uptake in PDAC have not been adequately assessed. We investigated ALA-induced porphyrin fluorescence in PDAC cell lines CFPAC-1 and PANC-1 and pancreatic ductal cell line H6c7 following incubation with 0.25-1.0 mM ALA for 4-48 h. Fluorescence was assessed qualitatively by microscopy and quantitatively by plate reader and flow cytometry. Haem biosynthesis enzymes and transporters were measured by quantitative polymerase chain reaction (qPCR). CFPAC-1 cells exhibited intense fluorescence under microscopy at low concentrations whereas PANC-1 cells and pancreatic ductal cell line H6c7 showed much lower fluorescence. Quantitative fluorescence studies demonstrated fluorescence saturation in the two PDAC cell lines at 0.5 mM ALA, whereas H6c7 cells showed increasing fluorescence with increasing ALA. Based on the PDAC:H6c7 fluorescence ratio studies, lower ALA concentrations provide better contrast between PDAC and benign pancreatic cells. Studies with qPCR showed upregulation of ALA influx transporter PEPT1 in CFPAC-1, whereas PANC-1 upregulated the efflux transporter ABCG2. We conclude that PEPT1 and ABCG2 expression may be key contributory factors for variability in ALA-induced fluorescence in PDAC.

Recent advances in the epidemiology and genetics of acute intermittent porphyria

Acute intermittent porphyria (AIP) is a dominant inherited disorder with a low penetrance that is caused by mutations in the gene coding for hydroxymethylbilane synthase (HMBS). Information about the epidemiology and molecular genetic features of this rare disorder is crucial to clinical research, and particularly to the evaluation of new treatments. Variations in the prevalence and penetrance of AIP in various studies may due to the different inclusion criteria and methods of assessment. Here, the prevalence and penetrance of AIP are analyzed systematically, and the genetic traits of different populations and findings regarding the genotype-phenotype correlation are summarized. In addition, quite a few studies have indicated that AIP susceptibility was affected by other factors, such as modifying genes. Findings regarding possible modifying genes are documented here, helping to reveal the pathogenesis of and treatments for AIP. The status of research on AIP in China reveals the lack of epidemiological and genetic studies of the Chinese population, a situation that needs to be promptly remedied.

Porphyric Neuropathy: Pathophysiology, Diagnosis, and Updated Management

PURPOSE OF REVIEW

To review the peripheral neurological complications of the acute hepatic porphyrias, as well as the latest advances in their pathophysiology and management.

RECENT FINDINGS

The diagnosis of porphyric neuropathy remains challenging as varying neuropathic patterns are encountered depending on disease stage, including a non-length-dependent distribution pattern. The major pathophysiologic mechanism is δ-aminolevulinic acid (ALA)-induced neurotoxicity. The less restrictive blood-nerve barrier in the autonomic ganglia and myenteric plexus may explain the frequency of dysautonomic manifestations. Recently, a prophylactic small interfering RNA (siRNA)-based therapy that reduces hepatic ALA Synthase-1 mRNA was approved for patients with recurrent neuro-visceral attacks. Neurologists should appreciate the varying patterns of porphyric neuropathy. As with most toxin-induced axonopathies, long-term outcomes depend on early diagnosis and treatment. While the short-term clinical and biochemical benefits of siRNA-based therapy are known, its long-term effects on motor recovery, chronic pain, and dysautonomic manifestations are yet to be determined.

Key transporters leading to specific protoporphyrin IX accumulation in cancer cell following administration of aminolevulinic acid in photodynamic therapy/diagnosis

The administration of aminolevulinic acid allow the formation and accumulation of protoporphyrin IX specifically in cancer cells, which then lead to photocytotoxicity following light irradiation. This compound, when accumulated at high levels, could also be used in cancer diagnosis as it would emit red fluorescence when being light irradiated. The concentration of protoporphyrin IX is pivotal in ensuring the effectiveness of the therapy. Studies have been carried out and showed the importance of various transporters in regulating the amount of these substrates by controlling the transport of various related metabolites in and out of the cell. There are many transporters involved and their expression levels are dependent on various factors, such as oxygen availability and iron ions. It is also important to note that these transporters may also have different expression levels depending on their organ. Understanding the mechanisms and the roles of these transporters are essential to ensure maximum accumulation of protoporphyrin IX, leading to higher efficiency in photodynamic therapy/diagnosis. In this review, we would like to discuss the roles of various transporters in protoporphyrin IX accumulation and how their involvement directly affect cancerous microenvironment.

Possible utility of peptide-transporter-targeting [19F]dipeptides for visualization of the biodistribution of cancers by nuclear magnetic resonance imaging

Stable-isotope-labeled probes suitable for magnetic resonance imaging (MRI) would have various potential medical applications, such as tumor imaging. Here, with the aim of developing MRI probes targeting peptide transporters, we synthesized a series of [¹⁹F]dipeptides by introducing one or two fluorine atoms or a trifluoromethyl group into the benzene ring of l-phenylalanyl-ψ[CS-N]-l-alanine (Phe-ψ-Ala), which is resistant to cleavage by peptidases. The mono- and difluoro dipeptides were efficiently transported by PEPT1 and PEPT2. Moreover, (3,5)-difluoro Phe-ψ-Ala was metabolically stable in human hepatocyte culture, and had a low distribution volume in mice. An acute toxicity study in mice revealed no apparent effect on body weight or behavior. The biodistribution and biodynamics of this compound could be clearly visualized by ¹⁹F-MRI in vivo, although specific signal enhancement was observed only in the bladder, but not in the tumor of tumor-xenografted mice. Although there was no specific signal enhancement of the tested compound at the tumor, the present study provides some challenging points regarding ¹⁹F-MRI probes for future investigation.

Uptake Transporters of the SLC21, SLC22A, and SLC15A Families in Anticancer Therapy-Modulators of Cellular Entry or Pharmacokinetics?

Solute carrier transporters comprise a large family of uptake transporters involved in the transmembrane transport of a wide array of endogenous substrates such as hormones, nutrients, and metabolites as well as of clinically important drugs. Several cancer therapeutics, ranging from chemotherapeutics such as topoisomerase inhibitors, DNA-intercalating drugs, and microtubule binders to targeted therapeutics such as tyrosine kinase inhibitors are substrates of solute carrier (SLC) transporters. Given that SLC transporters are expressed both in organs pivotal to drug absorption, distribution, metabolism, and elimination and in tumors, these transporters constitute determinants of cellular drug accumulation influencing intracellular drug concentration required for efficacy of the cancer treatment in tumor cells. In this review, we explore the current understanding of members of three SLC families, namely SLC21 (organic anion transporting polypeptides, OATPs), SLC22A (organic cation transporters, OCTs; organic cation/carnitine transporters, OCTNs; and organic anion transporters OATs), and SLC15A (peptide transporters, PEPTs) in the etiology of cancer, in transport of chemotherapeutic drugs, and their influence on efficacy or toxicity of pharmacotherapy. We further explore the idea to exploit the function of SLC transporters to enhance cancer cell accumulation of chemotherapeutics, which would be expected to reduce toxic side effects in healthy tissue and to improve efficacy.

Blood-Brain Barrier, Blood-Brain Tumor Barrier, and Fluorescence-Guided Neurosurgical Oncology: Delivering Optical Labels to Brain Tumors

Recent advances in maximum safe glioma resection have included the introduction of a host of visualization techniques to complement intraoperative white-light imaging of tumors. However, barriers to the effective use of these techniques within the central nervous system remain. In the healthy brain, the blood-brain barrier ensures the stability of the sensitive internal environment of the brain by protecting the active functions of the central nervous system and preventing the invasion of microorganisms and toxins. Brain tumors, however, often cause degradation and dysfunction of this barrier, resulting in a heterogeneous increase in vascular permeability throughout the tumor mass and outside it. Thus, the characteristics of both the blood-brain and blood-brain tumor barriers hinder the vascular delivery of a variety of therapeutic substances to brain tumors. Recent developments in fluorescent visualization of brain tumors offer improvements in the extent of maximal safe resection, but many of these fluorescent agents must reach the tumor via the vasculature. As a result, these fluorescence-guided resection techniques are often limited by the extent of vascular permeability in tumor regions and by the failure to stain the full volume of tumor tissue. In this review, we describe the structure and function of both the blood-brain and blood-brain tumor barriers in the context of the current state of fluorescence-guided imaging of brain tumors. We discuss features of currently used techniques for fluorescence-guided brain tumor resection, with an emphasis on their interactions with the blood-brain and blood-tumor barriers. Finally, we discuss a selection of novel preclinical techniques that have the potential to enhance the delivery of therapeutics to brain tumors in spite of the barrier properties of the brain.

TSPO2 translocates 5-aminolevulinic acid into human erythroleukemia cells

BACKGROUND

5-Aminolevulinic acid (ALA) is the first precursor of heme biosynthesis pathway. The exogenous addition of ALA to cells leads to protoporphyrin IX (PPIX) accumulation that has been exploited in photodynamic diagnostic and photodynamic therapy. Several types of ALA transporters have been described depending on the cell type, but there was no clear entry pathway for erythroid cells. The 18 kDa translocator protein (TSPO) has been proposed to be involved in the transport of porphyrins and heme analogs.

RESULTS

ALA-induced PPIX accumulation in erythroleukemia cells (UT-7 and K562) was impaired by PK 11195, a competitive inhibitor of both transmembrane proteins TSPO (1 and 2). PK 11195 did not modify the activity of the enzymes of heme biosynthesis, suggesting that ALA entry at the plasma membrane was the limiting factor. In contrast, porphobilinogen (PBG)-induced PPIX accumulation was not affected by PK 11195, suggesting that plasma membrane TSPO2 is a selective transporter of ALA. Overexpression of TSPO2 at the plasma membrane of erythroleukemia cells increased ALA-induced PPIX accumulation, confirming the role of TSPO2 in the import of ALA into the cells.

CONCLUSIONS

ALA-induced PPIX accumulation in erythroid cells involves TSPO2 as a selective translocator through the plasma membrane.

SIGNIFICANCE

This is the first characterisation of molecular mechanisms involving a new actor in ALA transport in ALA-induced PPIX accumulation in erythroleukemia cells, which could be inhibited by specific drug ligands.

New aspects of amino acid metabolism in cancer

An abundant supply of amino acids is important for cancers to sustain their proliferative drive. Alongside their direct role as substrates for protein synthesis, they can have roles in energy generation, driving the synthesis of nucleosides and maintenance of cellular redox homoeostasis. As cancer cells exist within a complex and often nutrient-poor microenvironment, they sometimes exist as part of a metabolic community, forming relationships that can be both symbiotic and parasitic. Indeed, this is particularly evident in cancers that are auxotrophic for particular amino acids. This review discusses the stromal/cancer cell relationship, by using examples to illustrate a number of different ways in which cancer cells can rely on and contribute to their microenvironment - both as a stable network and in response to therapy. In addition, it examines situations when amino acid synthesis is driven through metabolic coupling to other reactions, and synthesis is in excess of the cancer cell's proliferative demand. Finally, it highlights the understudied area of non-proteinogenic amino acids in cancer metabolism and their potential role.

The Cisplatin-Derived Increase of Mitochondrial Reactive Oxygen Species Enhances the Effectiveness of Photodynamic Therapy via Transporter Regulation

Photodynamic therapy (PDT) is a cancer treatment involving the generation of reactive oxygen species (ROS) by laser irradiation of porphyrins that accumulate in cancer tissues. 5-aminolevulinic acid (ALA), a porphyrin precursor, is often used as a photosensitizer. ALA is imported into cells via peptide transporter 1 (PEPT1), and porphyrin is exported via ATP-binding cassette member 2 of subfamily G (ABCG2). Thus, cancer cell-specific porphyrin accumulation involves regulation of both transporters to enhance the ALA-PDT effect. We reported previously that mitochondrial ROS (mitROS) upregulated PEPT1 expression and downregulated ABCG2 expression. Therefore, we propose that increasing mitROS production will enhance ALA-PDT cytotoxicity. Cisplatin is a chemotherapeutic drug that induces intracellular ROS generation. In this study, we investigated whether cisplatin-increased mitROS production in gastric cancer cell lines (RGK36 and RGK45) enhanced the cytotoxicity of ALA-PDT by regulation the expression of both PEPT1 and ABCG2. The results showed that cisplatin increased intracellular mitROS production in cancer but not normal cells (RGM1). PEPT1 was upregulated and ABCG2 downregulated in cancer cells treated with cisplatin. Moreover, intracellular porphyrin accumulation and ALA-PDT cytotoxicity increased. We conclude that cisplatin treatment increases the intracellular mitROS concentration and upregulates PEPT1 and downregulates ABCG2 expression.

In order for the light to shine so brightly, the darkness must be present-why do cancers fluoresce with 5-aminolaevulinic acid?

Photodynamic diagnosis and therapy have emerged as a promising tool in oncology. Using the visible fluorescence from photosensitisers excited by light, clinicians can both identify and treat tumour cells in situ. Protoporphyrin IX, produced in the penultimate step of the haem synthesis pathway, is a naturally occurring photosensitiser that visibly fluoresces when exposed to light. This fluorescence is enhanced considerably by the exogenous administration of the substrate 5-aminolaevulinic acid (5-ALA). Significantly, 5-ALA-induced protoporphyrin IX accumulates preferentially in cancer cells, and this enhanced fluorescence has been harnessed for the detection and photodynamic treatment of brain, skin and bladder tumours. However, surprisingly little is known about the mechanistic basis for this phenomenon. This review focuses on alterations in the haem pathway in cancer and considers the unique features of the cancer environment, such as altered glucose metabolism, oncogenic mutations and hypoxia, and their potential effects on the protoporphyrin IX phenomenon. A better understanding of why cancer cells fluoresce with 5-ALA would improve its use in cancer diagnostics and therapies.

Mechanistic study of PpIX accumulation using the JFCR39 cell panel revealed a role for dynamin 2-mediated exocytosis

5-aminolevulinic acid (5-ALA) has recently been employed for photodynamic diagnosis (ALA-PDD) and photodynamic therapy (ALA-PDT) of various types of cancer because hyperproliferating tumor cells do not utilize oxidative phosphorylation and do not efficiently produce heme; instead, they accumulate protoporphyrin IX (PpIX), which is a precursor of heme that is activated by violet light irradiation that results in the production of red fluorescence and singlet oxygen. The efficiencies of ALA-PDD and ALA-PDT depend on the efficient cellular uptake of 5-ALA and the inefficient excretion of PpIX. We employed the JFCR39 cell panel to determine whether tumor cells originating from different tissues can produce and accumulate PpIX. We also investigated cellular factors/molecules involved in PpIX excretion by tumor cells with the JFCR39 cell panel. Unexpectedly, the expression levels of ABCG2, which has been considered to play a major role in PpIX extracellular transport, did not show a strong correlation with PpIX excretion levels in the JFCR39 cell panel, although an ABCG2 inhibitor significantly increased intracellular PpIX accumulation in several tumor cell lines. In contrast, the expression levels of dynamin 2, which is a cell membrane-associated molecule involved in exocytosis, were correlated with the PpIX excretion levels. Moreover, inhibitors of dynamin significantly suppressed PpIX excretion and increased the intracellular levels of PpIX. This is the first report demonstrating the causal relationship between dynamin 2 expression and PpIX excretion in tumor cells.

ABCG2 expression is related to low 5-ALA photodynamic diagnosis (PDD) efficacy and cancer stem cell phenotype, and suppression of ABCG2 improves the efficacy of PDD

Photodynamic diagnosis/therapy (PDD/PDT) are novel modalities for the diagnosis and treatment of cancer. The photosensitizer protoporphyrin IX is metabolized from 5-aminolevulinic acid (5-ALA) intracellularly, and PDD/PDT using 5-ALA have been approved in dermatologic malignancies and gliomas. However, the molecular mechanism that defines the efficacy of PDD/PDT is unknown. In this study, we analyzed the functions of ATP-binding cassette (ABC) transporters in PDD using 5-ALA. Most of the human gastrointestinal cancer line cells examined showed a homogenous staining pattern with 5-ALA, except for the pancreatic cancer line PANC-1, which showed heterogeneous staining. To analyze this heterogeneous staining pattern, single cell clones were established from PANC-1 cells and the expression of ABC transporters was assessed. Among the ABC transporter genes examined, ABCG2 showed an inverse correlation with the rate of 5-ALA-positive staining. PANC-1 clone #2 cells showed the highest level of ABCG2 expression and the lowest level of 5-ALA staining, with only a 0.6% positive rate. Knockdown of the ABCG2 gene by small interfering RNAs increased the positive rate of 5-ALA staining in PANC-1 wild-type and clone cells. Interestingly, PANC-1 clone #2 cells showed the high sphere-forming ability and tumor-formation ability, indicating that the cells contained high numbers of cancer stem cells (CSCs). Knockdown or inhibition of ABCG2 increased the rate of 5-ALA staining, but did not decrease sphere-forming ability. These results indicate that gastrointestinal cancer cell lines expressing high levels of ABCG2 are enriched with CSCs and show low rates of 5-ALA staining, but 5-ALA staining rates can be improved by inhibition of ABCG2.

Identification of PEPT2 as an important candidate molecule in 5-ALA-mediated fluorescence-guided surgery in WHO grade II/III gliomas

PURPOSE

5-aminolevulinic acid (5-ALA) fluorescence-guided surgery (FGS) appears to be a promising treatment for glioma. However, 5-ALA-mediated fluorescence cannot always be detected in grade II/III gliomas. We hypothesized that gene expression patterns in the Protoporphyrin IX (PpIX) synthesis pathway may be associated with intraoperative fluorescence status of grade II/III gliomas, and then attempted to identify the key molecule of 5-ALA-mediated fluorescence.

METHODS

Using 50 surgically obtained specimens, which were diagnosed as grade II and III gliomas, we analyzed gene expression within the PpIX synthesis pathway to identify candidate molecules according to intraoperative 5-ALA-mediated fluorescence status. The most likely candidate gene was selected and confirmed by protein expression analysis. To evaluate the biological function of the molecule in PpIX synthesis, functional analysis was performed using specific, small interference (si)RNA in the SW-1783 human grade III glioma cell line.

RESULTS

Among the genes involved in the porphyrin synthesis pathway, the mRNA expression of Peptide transporter 2 (PEPT2) in FGS fluorescence-positive gliomas was significantly higher than that in fluorescence-negative gliomas. Protein expression of PEPT2 was also significantly higher in the fluorescence-positive gliomas, which was confirmed by western blot analysis and immunofluorescence analysis. The siRNA-mediated downregulation of the mRNA and protein expression of PEPT2 led to decreased PpIX fluorescence intensity, as confirmed by fluorescence spectrum analysis.

CONCLUSIONS

The results suggest PEPT2 is an important candidate molecule in 5-ALA-mediated FGS in grade II/III gliomas. As the overexpression of PEPT2 was associated with higher PpIX fluorescence intensity, PEPT2 may improve fluorescence-guided resection in grade II/III gliomas.

Xenopus oocytes as a heterologous expression system for analysis of tight junction proteins

Claudins (cldns) represent the largest family of transmembrane tight junction (TJ) proteins, determining organ-specific epithelial barrier properties. Because methods for the analysis of multiple cldn interaction are limited, we have established the heterologous Xenopus laevis oocyte expression system for TJ protein assembly and interaction analysis. Oocytes were injected with cRNA encoding human cldn-1, -2, or -3 or with a combination of these and were incubated in pairs for interaction analysis. Immunoblotting and immunohistochemistry were performed, and membrane contact areas were analyzed morphometrically and by freeze fracture electron microscopy. Cldns were specifically detected in membranes of expressing oocytes, and coincubation of oocytes resulted in adhesive contact areas that increased with incubation time. Adjacent membrane areas revealed specific cldn signals, including "kissing-point"-like structures representing homophilic trans-interactions of cldns. Contact areas of oocytes expressing a combination markedly exceeded those expressing single cldns, indicating effects on adhesion. Ultrastructural analysis revealed a self-assembly of TJ strands and a cldn-specific strand morphology.-Vitzthum, C., Stein, L., Brunner, N., Knittel, R., Fallier-Becker, P., Amasheh, S. Xenopus oocytes as a heterologous expression system for analysis of tight junction proteins.

High-Throughput Imaging of PPIX Using Confocal Microscopy

Increases in levels of protoporphyrin IX (PPIX; a heme precursor) may be driven by xenobiotic induction of aminolevulinic acid synthase 1 (ALAS1) expression. ALAS1 is the rate-limiting enzyme of heme biosynthesis and may be upregulated to satisfy the increased need for heme in CYP450 enzymes. Therefore, a high-throughput fluorescence spectroscopy method that detects PPIX would enable the screening of drugs that increase ALAS1 through nuclear hormone receptor-mediated induction of transcription that may cause toxicity or even provide utility in the diagnosis or treatment of cancers that have elevated cellular PPIX levels. This chapter describes a high-throughput plate-based imaging technique for determining cellular protoporphyrin levels by using the GE Healthcare InCell 6000 confocal imaging system to detect the presence and location of PPIX in each cell and may be adapted for use with other imaging systems. Laser excitation and a scientific-grade complementary metal oxide semiconductor (CMOS) camera generate short exposure times, decreasing photobleaching in the target cells that may result in inaccurate measurements of PPIX and increasing screening throughput. Nuclear staining was detected by using a laser with 405-nm excitation and 455-nm emission wavelengths, and the presence of PPIX was measured using 405-nm excitation and 706-nm emission wavelengths. Image analysis involving top-hat segmentation on both nuclear and PPIX staining was performed by using the InCell Analyzer Workstation software. This assay may be adapted to screen for PPIX formation, degradation, and transportation effectors. Indeed, the inclusion of PPIX transport inhibition would be expected to further widen the linear range of fluorescence and improve the method.

5-Aminolevulinic acid-mediated photodynamic therapy can target human glioma stem-like cells refractory to antineoplastic agents

BACKGROUND

Glioblastoma (GBM) is a highly malignant lethal brain cancer. Accumulated evidence suggests that elevated resistance of GBM to both chemo- and radio-therapy is, at least in part, due to the presence of a small population of glioma stem cells (GSC). In the present study, we aimed to determine the sensitivity of GSCs to 5-aminolevulinic acid-mediated photodynamic therapy (ALA-PDT).

METHODS

For this purpose, we established GSC-enriched cell cultures (termed glioma stem-like cells or GSLCs) from A172 human GBM cell line. Under our cultivation conditions, GSLCs formed floating spheroid clusters that contained increased population of CD133/Sox2 expressing cells. Firstly, to compare the activity of protoporphyrin IX (PpIX) biosynthesis in the GSLCs and the parental A172 glioma cells, we examined the expression levels of biosynthesis enzymes and transporters for PpIX using qRT-PCR, and investigated the intracellular levels of PpIX with use of flow cytometry analysis. Then, we evaluated the sensitivity of these cells to ALA-PDT in vitro. Finally, to confirm the therapeutic impact of ALA-PDT on GSLCs with more clinically relevant model, we performed the same experiment using three different patient-derived glioma sphere lines, which cultivated them either in stem cell media or under differentiation conditions in the presence of serum.

RESULTS AND CONCLUSION

GSLCs expressed higher mRNA levels of PpIX biosynthesis enzymes and its transporters PEPT1/2 and ABCB6, when compared to the parental A172 glioma cells. Consistently, flow cytometry analysis revealed that upon incubation with ALA, GSLCs accumulate a higher level of PpIX. Finally, we showed that GSLCs were more sensitive to ALA-PDT than the original A172 cells, and confirmed that all patient-derived glioma sphere lines also showed significantly increased sensitivity to ALA-PDT if cultivated under the pro-stem cell condition. Our data indicate that ALA-PDT has potential as a novel clinically useful treatment that might eliminate GBM stem cells that are highly resistant to current chemo- and radio-therapy.

Optical techniques for the diagnosis and treatment of lesions induced by the human papillomavirus - A resource letter

Human papillomaviruses (HPV) are the most common sexually-transmitted virus, and carcinogenic HPV strains are reported to be responsible for virtually all cases of cervical cancer and its precursor, the cervical intraepithelial neoplasia (CIN). About 30% of the sexually active population are considered to be affected by HPV. Around 600 million people are estimated to be infected worldwide. Diseases related to HPV cause significant impact from both the personal welfare point of view and public healthcare perspective. This resource letter collects relevant information regarding HPV-induced lesions and discusses both diagnosis and treatment, with particular attention to optical techniques and the challenges involved to the implementation of those approaches.

Function, Regulation, and Pathophysiological Relevance of the POT Superfamily, Specifically PepT1 in Inflammatory Bowel Disease

Mammalian members of the proton-coupled oligopeptide transporter family are integral membrane proteins that mediate the cellular uptake of di/tripeptides and peptide-like drugs and couple substrate translocation to the movement of H⁺ , with the transmembrane electrochemical proton gradient providing the driving force. Peptide transporters are responsible for the (re)absorption of dietary and/or bacterial di- and tripeptides in the intestine and kidney and maintaining homeostasis of neuropeptides in the brain. These proteins additionally contribute to absorption of a number of pharmacologically important compounds. In this overview article, we have provided updated information on the structure, function, expression, localization, and activities of PepT1 (SLC15A1), PepT2 (SLC15A2), PhT1 (SLC15A4), and PhT2 (SLC15A3). Peptide transporters, in particular, PepT1 are discussed as drug-delivery systems in addition to their implications in health and disease. Particular emphasis has been placed on the involvement of PepT1 in the physiopathology of the gastrointestinal tract, specifically, its role in inflammatory bowel diseases. © 2018 American Physiological Society. Compr Physiol 8:731-760, 2018.

Porphyria and kidney diseases

The kidneys, after the bone marrow and liver, are third in terms of the amounts of haem synthesized daily. Haem is incorporated into haemoproteins that are critical to renal physiology. In turn, disturbances in haem metabolism interfere with renal physiology and are tightly interrelated with kidney diseases. Acute intermittent porphyria causes kidney injury, whereas medical situations associated with end-stage renal disease, such as porphyrin accumulation, iron overload and hepatitis C, participate in the inhibition of uroporphyrinogen decarboxylase and predispose the individual to porphyria cutanea tarda. Even if some of these interactions have been known for a long time, the clinical situations associated with these interrelations have strikingly evolved over time with the advent of new therapeutic strategies for dialysis therapy and a better understanding of the pathophysiological mechanisms of porphyria-associated kidney disease. Physicians should be aware of these interactions. The aim of this review is to summarize the complex interactions between kidney physiology and pathology in the settings of porphyria and to emphasize their often-underestimated importance.

Novel potential photodynamic therapy strategy using 5-Aminolevulinic acid for ovarian clear-cell carcinoma

BACKGROUND

Photodynamic therapy (PDT) is known as a minimally invasive treatment for cancer. 5-Aminolevulinic acid (ALA) is a precursor of the photosensitizing agent protoporphyrin IX (PpIX). Patients with ovarian clear-cell carcinoma (CCC) have poorer prognoses than those of patients with other histological CCC types. We evaluated the efficacy of ALA-PDT on CCC cells in vitro.

METHODS

We used seven human CCC cell lines to measure the cytotoxicity of ALA-PDT. PpIX production in cancer cells was measured using a micro-plate reader. Quantitative real-time PCR was performed to assess the mRNA levels of genes involved in the accumulation of PpIX in cancer cells. Additionally, we measured the enhancement in cytotoxicity with the use of an ABCG2 inhibitor.

RESULTS

We found that three cell lines were highly sensitive to ALA-PDT. In contrast, one cell line was resistant to ALA-PDT. The cytotoxicity of ALA-PDT varied among CCC cell lines. The IC50 values of ALA-PDT for the CCC cell lines had a wide range (30-882μM). The cytotoxicity of ALA-PDT was correlated with the intracellular PpIX accumulation. The cell lines sensitive to ALA-PDT expressed PEPT1 (an ALA uptake transporter). The cell line resistant to ALA-PDT expressed ABCG2 (a PpIX export transporter). In the resistant cell line, a combination treatment with both ALA and an ABCG2 inhibitor resulted in the promotion of cytotoxic sensitivity.

CONCLUSION

The present study revealed the efficacy of ALA-PDT against CCC with chemoresistance in vitro.

Oligopeptide Transport in Rat Lung Alveolar Epithelial Cells is Mediated by Pept2

PURPOSE

Studies were conducted in primary cultured rat alveolar epithelial cell monolayers to characterize peptide transporter expression and function.

METHODS

Freshly isolated rat lung alveolar epithelial cells were purified and cultured on permeable support with and without keratinocyte growth factor (KGF). Messenger RNA and protein expression of Pept1 and Pept2 in alveolar epithelial type I- and type II-like cell monolayers (±KGF, resp.) were examined by RT-PCR and Western blotting. ³H-Glycyl-sarcosine (³H-gly-sar) transmonolayer flux and intracellular accumulation were evaluated in both cell types.

RESULTS

RT-PCR showed expression of Pept2, but not Pept1, mRNA in both cell types. Western blot analysis revealed presence of Pept2 protein in type II-like cells, and less in type I-like cells. Bi-directional transmonolayer ³H-gly-sar flux lacked asymmetry in transport in both types of cells. Uptake of ³H-gly-sar from apical fluid of type II-like cells was 7-fold greater than that from basolateral fluid, while no significant differences were observed from apical vs. basolateral fluid of type I-like cells.

CONCLUSIONS

This study confirms the absence of Pept1 from rat lung alveolar epithelium in vitro. Functional Pept2 expression in type II-like cell monolayers suggests its involvement in oligopeptide lung disposition, and offers rationale for therapeutic development of di/tripeptides, peptidomimetics employing pulmonary drug delivery.

Doxycycline potentiates antitumor effect of 5-aminolevulinic acid-mediated photodynamic therapy in malignant peripheral nerve sheath tumor cells

Neurofibromatosis type 1 (NF1) is one of the most common neurocutaneous disorders. Some NF1 patients develop benign large plexiform neurofibroma(s) at birth, which can then transform into a malignant peripheral nerve sheath tumor (MPNST). There is no curative treatment for this rapidly progressive and easily metastatic neurofibrosarcoma. Photodynamic therapy (PDT) has been developed as an anti-cancer treatment, and 5-aminolevulinic (ALA) mediated PDT (ALA-PDT) has been used to treat cutaneous skin and oral neoplasms. Doxycycline, a tetracycline derivative, can substantially reduce the tumor burden in human and animal models, in addition to its antimicrobial effects. The purpose of this study was to evaluate the effect and to investigate the mechanism of action of combined doxycycline and ALA-PDT treatment of MPNST cells. An 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay showed that the combination of ALA-PDT and doxycycline significantly reduce MPNST survival rate, compared to cells treated with each therapy alone. Isobologram analysis showed that the combined treatment had a synergistic effect. The increased cytotoxic activity could be seen by an increase in cellular protoporphyrin IX (PpIX) accumulation. Furthermore, we found that the higher retention of PpIX was mainly due to increasing ALA uptake, rather than activity changes of the enzymes porphobilinogen deaminase and ferrochelatase. The combined treatment inhibited tumor growth in different tumor cell lines, but not in normal human Schwann cells or fibroblasts. Similarly, a synergistic interaction was also found in cells treated with ALA-PDT combined with minocycline, but not tetracycline. In summary, doxycycline can potentiate the effect of ALA-PDT to kill tumor cells. This increased potency allows for a dose reduction of doxycycline and photodynamic radiation, reducing the occurrence of toxic side effects in vivo.

Influence of peptide transporter 2 (PEPT2) on the distribution of cefadroxil in mouse brain: A microdialysis study

Peptide transporter 2 (PEPT2) is a high-affinity low-capacity transporter belonging to the proton-coupled oligopeptide transporter family. Although many aspects of PEPT2 structure-function are known, including its localization in choroid plexus and neurons, its regional activity in brain, especially extracellular fluid (ECF), is uncertain. In this study, the pharmacokinetics and regional brain distribution of cefadroxil, a β-lactam antibiotic and PEPT2 substrate, were investigated in wildtype and Pept2 null mice using in vivo intracerebral microdialysis. Cefadroxil was infused intravenously over 4h at 0.15mg/min/kg, and samples obtained from plasma, brain ECF, cerebrospinal fluid (CSF) and brain tissue. A permeability-surface area experiment was also performed in which 0.15mg/min/kg cefadroxil was infused intravenously for 10min, and samples obtained from plasma and brain tissues. Our results showed that PEPT2 ablation significantly increased the brain ECF and CSF levels of cefadroxil (2- to 2.5-fold). In contrast, there were no significant differences between wildtype and Pept2 null mice in the amount of cefadroxil in brain cells. The unbound volume of distribution of cefadroxil in brain was 60% lower in Pept2 null mice indicating an uptake function for PEPT2 in brain cells. Finally, PEPT2 did not affect the influx clearance of cefadroxil, thereby, ruling out differences between the two genotypes in drug entry across the blood-brain barriers. These findings demonstrate, for the first time, the impact of PEPT2 on brain ECF as well as the known role of PEPT2 in removing peptide-like drugs, such as cefadroxil, from the CSF to blood.

A Variant of Peptide Transporter 2 Predicts the Severity of Porphyria-Associated Kidney Disease

CKD occurs in most patients with acute intermittent porphyria (AIP). During AIP, δ-aminolevulinic acid (ALA) accumulates and promotes tubular cell death and tubulointerstitial damage. The human peptide transporter 2 (PEPT2) expressed by proximal tubular cells mediates the reabsorption of ALA, and variants of PEPT2 have different affinities for ALA. We tested the hypothesis that PEPT2 genotypes affect the severity and prognosis of porphyria-associated kidney disease. We analyzed data from 122 individuals with AIP who were followed from 2003 to 2013 and genotyped for PEPT2 At last follow-up, carriers of the PEPT2*1*1 genotype (higher affinity variant) exhibited worse renal function than carriers of the lower affinity variants PEPT2*1/*2 and PEPT2*2/*2 (mean±SD eGFR: 54.4±19.1, 66.6±23.8, and 78.1±19.9 ml/min per 1.73 m², respectively). Change in eGFR (mean±SD) over the 10-year period was -11.0±3.3, -2.4±1.9, and 3.4±2.6 ml/min per 1.73 m² for PEPT2*1/*1, PEPT2*1*2, and PEPT*2*2*2 carriers, respectively. At the end of follow-up, 68% of PEPT2*1*1 carriers had an eGFR<60 ml/min per 1.73 m², compared with 37% of PEPT2*1*2 carriers and 15% of PEPT2*2*2 carriers. Multiple regression models including all confounders indicated that the PEPT2*1*1 genotype independently associated with an eGFR<60 ml/min per 1.73 m² (odds ratio, 6.85; 95% confidence interval, 1.34 to 46.20) and an annual decrease in eGFR of >1 ml/min per 1.73 m² (odds ratio, 3.64; 95% confidence interval, 1.37 to 9.91). Thus, a gene variant is predictive of the severity of a chronic complication of AIP. The therapeutic value of PEPT2 inhibitors in preventing porphyria-associated kidney disease warrants investigation.

Selective 5-aminolevulinic acid-induced protoporphyrin IX fluorescence in Gliomas

Malignant gliomas are locally invasive tumors that offer a poor prognosis. Evidence shows that complete resection of the tumor at the time of surgery confers a significant improvement in overall survival. In recent years, 5- aminolevulinic acid (ALA)-induced fluorescence has been used by neurosurgeons to good effect in increasing the rate of complete resection. Despite the considerable interest in the use of 5-ALA in fluorescence-guided neurosurgery, the mechanisms behind the accumulation of Protoporphyrin IX (PpIX) in neoplastic tissue are unclear. In this review, we summarize the evidence in the literature on the mechanisms underlying the selective production of PpIX with a specific focus on gliomas.

Substrates of the human oligopeptide transporter hPEPT2

Oligopeptide transporters serve important functions in nutrition and pharmacology. In particular, these transporters help maintain the homeostasis of peptides. The peptide-transporter PEPT2 is a high-affinity and low-capacity type oligopeptide transporter from the proton-coupled oligopeptide transporter family. PEPT2 has recently received attention because of its potential application in targeted drug delivery. PEPT2 is widely distributed in kidney, central nervous system, and lung of organisms. In general, all dipeptides, tripeptides, and peptide-like drugs such as β-lactam antibiotics and angiotensin-converting enzyme inhibitors could be mediated and transported as a substrate of PEPT2. The design of many extant drugs and prodrugs is based on the substrate structure of PEPT2 to accelerate absorption via peptide transporters. Thus, this paper summarizes the substrate features of PEPT2 to promote the rational design of drugs and prodrugs that target peptide transporters.

The proton-coupled oligopeptide transporter 1 plays a major role in the intestinal permeability and absorption of 5-aminolevulinic acid

BACKGROUND AND PURPOSE

5-Aminolevulinic acid (5-ALA) has been widely used in photodynamic therapy and immunofluorescence of tumours. In the present study, the intestinal permeability and oral pharmacokinetics of 5-ALA were evaluated to probe the contribution of the proton-coupled oligopeptide transporter 1 (PEPT1) to the oral absorption and systemic exposure of this substrate.

EXPERIMENTAL APPROACH

In situ single-pass intestinal perfusions and in vivo oral pharmacokinetic studies were performed in wildtype and Pept1 knockout mice. Perfusion studies were performed as a function of concentration dependence, specificity and permeability of 5-ALA in different intestinal segments. Pharmacokinetic studies were performed after 0.2 and 2.0 μmoL·g(-1) doses of 5-ALA.

KEY RESULTS

The permeability of 5-ALA was substantial in duodenal, jejunal and ileal regions of wildtype mice, but the residual permeability of 5-ALA in the small intestine from Pept1 knockout mice was only about 10% of that in wildtype animals. The permeability of 5-ALA in jejunum was specific for PEPT1 with no apparent contribution of other transporters, including the proton-coupled amino acid transporter 1 (PAT1). After oral dosing, the systemic exposure of 5-ALA was reduced by about twofold during PEPT1 ablation, and the pharmacokinetics were dose-proportional after the 0.2 and 2.0 µmol·g(-1) doses. PEPT1 had a minor effect on the disposition and peripheral tissue distribution of 5-ALA.

CONCLUSION AND IMPLICATIONS

Our findings suggested a major role of PEPT1 in the intestinal permeability and oral absorption of 5-ALA. In contrast, another proton-coupled transporter, PAT1, appeared to play a limited role, at best.